They are not put in backwards either? Some electrolytics have confusing polarity indicators.

And thanks for the link

10µF, 63V. Long pin positive, negative indicated on cap body. These are definitely in the correct orientation (as per silkscreen). I triple check with all polarised components - it's an OCD thing I have.

it is wicked as he said. all 4 VCOs show the same weird misbehaviour, on two different PSUs...

so IMHO this is not an error n the VCO builds. 4 times the same single error i mean. it has to be something general that applies to all 4 builds, or to both PSUs. wrong parts, wiring...
that it is getting worse over time is irritating. it is not a working/not working situation.

it is wicked as he said. all 4 VCOs show the same weird misbehaviour, on two different PSUs...

so IMHO this is not an error n the VCO builds. 4 times the same single error i mean. it has to be something general that applies to all 4 builds, or to both PSUs. wrong parts, wiring...
that it is getting worse over time is irritating. it is not a working/not working situation.

the electrolytics are the 1st promising scent, though.

I'm going to order some more caps from a different outlet. Maybe I have a bad batch... Just an idea of course, even though I have not noticed problems in any other applications I've used them in._________________

I'm going to order some more caps from a different outlet. Maybe I have a bad batch... Just an idea of course, even though I have not noticed problems in any other applications I've used them in.

Good plan IMO ... long pin + and - indicated on body .. checked a couple here, they are like that.

I can think of a couple of reasons for electrolytes to go defect ... too high a voltage, put in backwards or too much AC -- in the latter case you'd have terrible hum problems though. Just to be sure you could check your power lines with the scope,

i have had one bottle of tempranillo tonight, and i have the feeling that the reason is so simple, yet hidden. as soon as it became obvious everyone would say: so clear! what else!
alas, we are still one step before that revalation...

i have had one bottle of tempranillo tonight, and i have the feeling that the reason is so simple, yet hidden. as soon as it became obvious everyone would say: so clear! what else!
alas, we are still one step before that revalation...

what 4046 are you using? maybe i should mail you a good NXP one?

If you could that would be awesome. Naturally I'll pay for the chip and postage. I'll PM you about it._________________

Just a thought about electrolytic caps, I had read some years ago about a Chinese manufacturer that had gotten stolen manufacturing process plans from an American mfr, but the stolen plans were missing one page of instructions. The capacitors were made without one of the required chemical processes. These capacitors would work - for a while and then fail. I'm wondering if somehow some old stock of those is still running around or if the plans were sold to someone else? The idea of a different mfr sounds like a good idea. And also the idea of a different stock of 4046. The X-4046 design ought to be quite solid coming from TH. Please let us know what the final answer is._________________FPGA, dsPIC and Fatman Synth Stuff

Time flies like a banana.Fruit flies when you're having fun.BTW, Do these genes make my ass look fat?corruptio optimi pessima

Just a thought about electrolytic caps, I had read some years ago about a Chinese manufacturer that had gotten stolen manufacturing process plans from an American mfr, but the stolen plans were missing one page of instructions. The capacitors were made without one of the required chemical processes. These capacitors would work - for a while and then fail.

Just a thought about electrolytic caps, I had read some years ago about a Chinese manufacturer that had gotten stolen manufacturing process plans from an American mfr, but the stolen plans were missing one page of instructions. The capacitors were made without one of the required chemical processes. These capacitors would work - for a while and then fail.

this is a great story to share!

LektroD, a proven NXP is on it's way to you: in a antistatic box within a box

This is so very much appreciated. I really hope this works and answers all my questions.

So far I have replaced the power caps with different manufacturers, replaced all chips (except 4046), if this doesn't resolve it, I will have to look at the other components, such as the box capacitors, resistors & transistors, as that's all that's left..._________________

I've just got back from visiting my family and arrived to find a package with a 4046 waiting for me (many thanks Matthias). I eagerly got to work replacing the chip with the new NXP model, and guess what...

*drum roll*

The problem still persists...

On the bright side, it has eliminated one more possible cause, but I really have no idea what else to try now..._________________

maybe four eyes see more than just two? you could mail me one of these troublemakers...

Thank you for offering to take the time to do this for me. I'll wait until the SSM2210's arrive first, see if that fixes the problem. If not and I cant resolve it by every means I've tried then I will probably ship one over to you. They are hardwired, so I'll have to send them as a module (5U).

Am I right in understanding that originally, all 4 oscillators were stable, but have become unstable over time? And that the instability manifests as a minor random variation in pitch(not eg four octave jumps).

I couldn't hear any periodicity in the variation in the sample you posted. Does an FTT analysis show any - could you compare one with that for a stable VCO? (I'm looking to whether the problem is random - which would suggest, though not confirm, a noise issue, or has any periodicity, which might point something thermo-mechanical?

Can you run a module off a battery supply - to eliminate noise either in either of your PSUs or the mains as a cause. (White noise on the ground suggests itself?) Also, take it somewhere else, turn off as much nearby mains equipment as possible. (To check it isn't caused by something in the local electric environment)

I assume you've checked the current draw isn't excessive?

The gradual development of the problem is really puzzling. And it sounds as if it developed at different times, and different rates, in all four modules (so it's not, for example, a deterioration in your mains supply).

I don't see that it can be a problem with soldering, affecting four boards the same way. What about the board material itself - could that have changed over time (baked in the long hot UK summer?)

Are you using some form of VC to get the freq or are you just using the course and fine tune knobs to set the freq with no VC? What I'm trying to say is if you're using VC to control the oscs are you sure that isn't bad?

Have you added any digital modules that have high freq clocks and signals. Could be some form of EFI or PS noise. Or did you add any modules about the time things went south. Might try disconnection them.

Have you checked the sync? Might be getting some random sync pulses that are resetting the osc.

Are you using some form of VC to get the freq or are you just using the course and fine tune knobs to set the freq with no VC? What I'm trying to say is if you're using VC to control the oscs are you sure that isn't bad?

The first thing I did was test the oscillators independently (also with waveshaper removed). I also earthed the CV ins to make sure they weren't the cause.

Quote:

Have you added any digital modules that have high freq clocks and signals. Could be some form of EFI or PS noise. Or did you add any modules about the time things went south. Might try disconnection them.

All analogue system.

Quote:

Have you checked the sync? Might be getting some random sync pulses that are resetting the osc.

Not sure where on the PCB to test the sync?

I'm waiting for the SSM2210's to arrive. I have a feeling if the hand matched transistors have become bad somehow, each of the transistors will be pulling frequencies from each other thus making it unstable. I'll wait and see what happens once the SSM2210's arrive._________________

Have you checked the sync? Might be getting some random sync pulses that are resetting the osc.

Not sure where on the PCB to test the sync?

I'm wondering if the sync is randomly triggering changing the freq. I've worked on several circuits that have had problem in that area. I hope that you have an oscilloscope which would make things easy.

I'm using sheet 1 of the schematics for reference. I'd look around the XOR gate in the 4046 which are pins 3, 14, 2 and 5. First I would check the junction of Q3s' collector and R14, pin 3 of the 4046 would work for that. It should be high. Next check pin 14 of the 4046 and make sure it is high. Lastly I'd check pin 2 and 5, they should be low. Look for noise or very narrow pulses on the signals.

If you don't have a digital storage scope that can capture glitches or narrow pulses there is another trick you can do. What you can do is use an one shot trigger if you scope has it. On most modern scopes you can set them up to do a single trigger and stop. Usually they have some form of indication (lamp, LED) to show that the trigger has occurred. Set the trigger voltage for either a logic high or low (what ever you need to test for). Then check the indicator to see if it has triggered. You can go away and come back latter to see if it has triggered too.

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